Through the combined use of the experimental methodologies of somatic cell genetics and DNA recombinant research, we have isolated several recombinant clones that include non-repeated DNA sequences homologous to specific regions of the human-X. In addition, we have obtained from other investogators six gene-specific cDNA clones (OTC,PGK, HGPRT, G6PD, FVIII, and FIX) and several genomic clones mapping to well spread sites along the short and long arm of the human-X. The aim of the present long term project is to use such array of molecular probes to screen for X-linked restriction enzyme length polymorphisms (X-RFLP) among the progenitors of three-generation Sardinian pedigrees that segregate already for two or more common X-linked polymorphisms or for some of these and rare X-linked mutants. From the work thus far caried out it appears that many of these pedigrees may segregate also for one or more X-DNA variants detected by the above mentioned probes. This will allow a rapid accumulation of data on the linkage relationship between specific X-RFLPs and/or between some of these and other common or rare X-linked mutants. Besides the straightforward Lod-score analysis we plan to gather data on the subregional mapping and the relative order of newly discovered X-RLPs from their segregation in our large series of "recombinant" and "X-non-disjunction" families. In turn, the segregation of X-RFLPs, already mapped to the two X-subtelomeric ends, is expected to resolve the order of the closely linked loci clustered in these regions, while new instances of common X-RFLPs, already mapped to the two X-subtelomeric ends, is expected to resolve the order of the closely linked loci clustered in these regions, while new instances of common X-RFLPs used in conjunction with two polymorphic markers of the X-centromere may provide new insights on the mechanisms of X-nondisjunction. Additional motivations for wanting to carry out the above mentioned studies are: (i) the easiness with which large three-generation pedigrees can be ascertained in this island and studied with full cooperation; (ii) the need of relying on "population" rather than "hospital" data when wanting to detect instances of genetic disequilibrium generated by close linkage or by mutations capable of suppressing crossing over. Thus, the ultimate goal of the project is not only to contribute to the biology of genetic recombination in humans (by comparing X-mapping data gathered with the cytologic, molecular, and /or genetic approach), but also to secure the immortalization of precious biological material that promises to be as useful to the human geneticists as mouse recombinant strains are to mouse geneticists.